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Altera_Forum
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12 years ago

Unused Differential I/O pins & External memory interface pins

Dear sir,

I am using Cyclone -IV E FPGA in my design.

This is regarding connecting "Unused Differential I/O pins & External memory interface pins" of cyclone IV FPGA E.

Please read the text from Cyclone® IV Device Family Pin Connection GuidelinesPCG-01008- 1.5 document

"When these IO pins are not used, they can be tied to gnd. See Note 12."

But the note 12 says

"the unused pins must be connected as specified in the quartus ii software settings. The default Quartus II setting for unused pins is 'As inputs tri-stated with weak pull-up resistors', unless for specific pins that Quartus II software connects them to GND automatically. To change the setting, go to 'Assignments', then 'Device'. Click on 'Device & Pin options' dialog box and go to 'Unused Pins' tab. You may choose the desired setting from the 'Reserve all unused pins' drop down list."

If I don't want to use the differential i/o pins & external memory interface pins, can they be left unconnected or tied to ground?

Please clarify.

Regards,

Thulasi

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    12 years ago

    I typically leave unused pins unconnected and then enable the weak pull-up. This is useful on BGA devices, as it allows you to use the vias near unused I/Os as ground or power vias for via-in-pad decoupling on the bottom of the FPGA.

    The problem with connecting I/O to ground is that you need to have a WARNING somewhere in the documentation not to drive unused pins to anything but ground ...

    Cheers,

    Dave